The present invention relates to a multi-frequency ultrasonic cleaning method and apparatus for improving a cleaning effect by emitting ultrasonic waves of multi-frequencies.
In the prior art, generally used cleaning apparatus (see FIG. 1), one vibrator 2 is attached at a bottom portion of a cleaning tank 1. When a signal of a resonance frequency of the vibrator 2 is applied from an oscillator 3 to the vibrator 2, an ultrasonic wave having the resonance frequency of the vibrator 2 is emitted from the vibrator 2 and the surface to be cleaned in the cleaning tank 1 are cleaned by the ultrasonic wave.
Because it is not easy to remove stain from the surface to be cleaned by using an ultrasonic wave of one frequency, a plurality of vibrators generating ultrasonic waves of different resonance frequencies are attached to the tank 1 and the stain which is not removed from the surface to be cleaned in the ultrasonic wave of the one frequency is removed by ultrasonic waves of different resonance frequencies.
In such cleaning apparatus, because a plurality of vibrators are attached to the cleaning tank 1, the cleaning tank 1 must be made adequately large, and since only the ultrasonic waves of the resonance frequencies of the respective vibrators are generated, a stain which is removed only by an ultrasonic wave of other frequencies except these frequencies is not removed by the above frequencies.
For supplying ultrasonic waves of multi-frequencies from one vibrator the applicant provided an asymmetric Langevin type vibrator 4 in which piezoelectric vibrators 5 and electrodes 5a and 5b are put between a long metal block 6 and a short metal block 7 and screw threads at both ends of a bolt not shown are engaged with screw threads of the metal blocks 6 and 7 (see FIGS. 2 and 3).
Three oscillators of different frequencies are connected through a switching circuit to the electrodes 5a and 5b of the vibrator 4 and this vibrator 4 can emit three ultrasonic waves of three frequencies every predetermined time intervals respectively.
Because the one vibrator 4 transmits ultrasonic waves of three different frequencies, the cleaning tank 1 can be formed small. However, only the three ultrasonic waves are transmitted from the vibrator 4, thus, the same as the prior art, so that stain removed by other frequencies are not removed by the three frequencies.